Boris Johnson today accused Tube and bus fare dodgers of being a "parasitic scourge" on London as figures showed the problem has got worse.

The cost of fare-dodging rose to almost £75 million last year, up £5 million from the previous year.

At least 120,000 passengers are known to have "dodged" their fare and Transport for London believes many hundreds of thousands of journeys are made each year by people with no valid ticket.

"Fare dodgers are a parasitic scourge on this city costing London millions of pounds," said the Mayor as TfL announced a clampdown on cheats, with more plain-clothes ticket inspectors and police operations. Inspectors and uniformed staff will target specific areas and routes with British Transport Police and City of London Police.

Mr Johnson also said that one of the main reasons he was phasing out "the dreaded bendy buses" was because "they made it far too easy for people to avoid paying".

Bendy buses have Oyster card readers by the rear doors and passengers do not have to pass the driver when boarding.

The Mayor said: "As out streets become bendy-free we are seeing some encouraging signs but these plain-clothed operations are a reminder to everyone using public transport that we expect them to pay their way."

London's buses lost £40 million and the Tube £20 million last year as a result of fare-dodging. One in four passengers believe it is "easy" to avoid paying and one in 10 said it was "worth the risk", according to a TfL survey.

Posters warn: "Plain clothes inspectors operate across our network. Get caught fare evading and risk a fine of up to £1,000 and a criminal record."

Last year TfL prosecuted 20,000 fare evaders and handed out more than 98,000 penalty fares of £50-a-time. More than 250 inspectors patrol the Tube and there are 220 on the buses.

A TfL spokesman put the increase in fare dodging down to record numbers of passengers on the Tube and buses. He said fare evasion had fallen on routes where bendy buses have been replaced.